The present invention relates in general to registration mechanisms for sheet transport apparatus, and more particularly, to a registration mechanism employing a pair of tandem frusto-conical rollers for effecting edge registration of a transported sheet.
In modern reproduction apparatus, such as printers or copiers or the like, information is reproduced on receiver members such as cut sheets of paper for example. Typically the receiver members are transported seriatim along a path and registered in the path so as to be located to receive a developed image-wise-pattern corresponding to the information to be reproduced. The developed image-wise pattern is transferred to the receiver member and fixed thereto to form the desired reproduction. The particular registration of the receiver member with the developed image-wise pattern is critical in forming an acceptable reproduction. In view of the accuracy of registration required in certain reproduction apparatus, it has been found necessary to provide for both in-track and cross-track alignment.
Registration apparatus which provide for cross-track alignment by the use of a frusto-conical roller are well known; see for example, U.S. Pat. No. 3,929,327, issued Dec. 30, 1975, in the name of Olson. As described in the above patent, the radial deformation of the frusto-conical roller exerts forces on a transported sheet to urge the sheet in the transport (in-track) direction as well as to provide a torque on the sheet to rotate the sheet into engagement with an elongated lateral registration edge. Continued transport of the sheet then causes the sheet to become aligned, in a direction transverse (cross-track) to the transport direction, against the elongated lateral registration edge. However, this arrangement requires substantial movement of the sheet in the transport direction before cross-track alignment is completed. In a reproduction apparatus operating at a relatively high speed with a short sheet travel path, there may not be enough travel distance to assure the desired cross-track alignment. Furthermore, the provision of the elongated lateral registration edge serves to impart friction forces to the sheet being aligned, and as a result may adversely impact the overall registration function of the registration apparatus.